C.sub.8 alkylaromatic hydrocarbons are generally considered to be valuable products, and para-xylene in particular is in high demand. On the other hand, C.sub.9 and C.sub.10 alkylaromatic hydrocarbons are not nearly as valuable but are typically produced as a byproduct in the same aromatic production processes used to produce C.sub.8 alkylaromatic hydrocarbons. Various approaches have been used to convert the less valuable C.sub.9 and C.sub.10 alkylaromatic hydrocarbons into C.sub.8 alkylaromatic hydrocarbons. One popular approach has been to transalkylate C. and C.sub.10 alkylaromatic hydrocarbons along with benzene or toluene to form the C.sub.8 alkylaromatic hydrocarbons. Specifically, trimethylbenzenes and tetramethylbenzenes have been transalkylated along with benzene and toluene to form xylenes. However, transalkylation reactions are equilibrium limited and the product contains a mixture of unreacted C.sub.9 and C.sub.10 alkylaromatic hydrocarbons along with the desired C.sub.8 alkylaromatic hydrocarbons. To increase conversion, commercial processes have utilized a two-stage design with the first stage being a fixed bed reactor and the second stage being a separation unit. Unreacted C.sub.9 and C.sub.10 alkylaromatic hydrocarbons present in the reactor product stream are separated and recycled to the reactor; see for example U.S. Pat. No. 3,211,798.
Once the C.sub.8 alkylaromatic hydrocarbons have been produced, they may need to be separated from the unreacted C.sub.9 and C.sub.10 alkylaromatic hydrocarbons. The present invention provides a process for separating the desired C.sub.8 alkylaromatic hydrocarbons from the less desired C.sub.9 and C.sub.10 alkylaromatic hydrocarbons using zeolite Y, or ion exchanged zeolite Y as an adsorbent. Zeolite Y has been used as an adsorbent in other applications such as the separation of the specific C.sub.8 alkylaromatic hydrocarbon isomers. For example, U.S. Pat. No. 4,255,607 discloses the separation of aromatic C.sub.8 isomers by adsorption, preferably contacting the mixture with zeolite Y and then developing the resulting adsorption bond with an ether having selectivity for para-xylene. Japanese Patent No. 79,037,129-B discloses contacting a mixture of C.sub.8 aromatic hydrocarbons with a Y-type zeolite containing sodium, calcium, cobalt and or strontium as cation to selectively adsorb meta-xylene. U.S. Pat. No. 4,079,094 discloses separating ethylbenzene from a mixture of xylene isomers by passing through a column of an adsorbent comprising type X or Y zeolite completely exchanged with strontium and potassium. The xylenes are selectively adsorbed and an ethylbenzene stream is withdrawn. U.S. Pat. No. 4,028,428 discloses separating ethylbenzene from a mixture of xylene isomers by contacting the mixture with an adsorbent of a strontiumexchanged type X or type Y zeolite. The xylenes are selectively adsorbed and ethylbenzene may be withdrawn. U.S. Pat. No. 3,998,901 discloses separating ethylbenzene from a mixture of xylene isomers under adsorption conditions with a type X or Y zeolite completely exchanged with strontium and potassium. U.S. Pat. No. 3,997,620 discloses para-xylene being separated from mixtures containing other C.sub.8 aromatics by contacting the mixture under adsorption conditions with type X or Y zeolite containing barium and strontium which selectively adsorbs the paraxylene.
The present invention solves a different problem from that of separating C.sub.8 alkylaromatic hydrocarbon isomers. Instead, the present invention is directed to at least one C.sub.8 alkylaromatic hydrocarbon from at least one C.sub.9 or C.sub.10 alkylaromatic hydrocarbon, which is a problem encountered in processes such as transalkylation.